By monitoring the input voltage, the reference generates a precise UVLO signal whose threshold voltage has little dependence to the temperature and technology change.

The results of the simulation show that the modulator has the characteristics of under- voltage protection, low start up current and dissipation by using the improved under-voltage lockout circuit and voltage reference.

Second, according to application requirement, the author designed the overall structural design of circuit, analyzed and designed the core blocks which included Schmitt Trigger, Dead Time, Undervoltage Latch, the Signal Output of High-Low side, Pulse Generation Circuit, Level Shift, Pulse Filter and RS Trigger.

The paper analyzed the existent problems for getting power source of pressure blocking circuit taken as example of the switches from Siemens and ABB,and put forward the corresponding solution method according to these problems.

When replacing operative boxes and disconnectors,the configuration problems of many relative circuits are discovered,such as pressure blocking,spring prevention,open-phase trip and so on.

However, without voltage blocking for the bus protection, it leads to weak anti-interference capability in 3/2 circuit breakers connection.

The feasibility and universality of the voltage blocking release approach is explained,which uses the AND logic of protection active and breaker current existence.